In general, a CMOS image sensor is manufactured by bonding a CMOS device made of silicon to a protective frame made of ceramic material and the like with an adhesive, and then electrically connecting the CMOS device to the protective frame. The CMOS device is fabricated by forming a photodiode as a semiconductor detection part, a charge coupled type transfer part including poly-silicon electrodes, an FET (field effect transistor) as a charge read-out part and the like on a semiconductor substrate by typical semiconductor processes.
The CMOS image sensor has a problem that when energy rays such as light and electrons are applied from the front surface side, the energy rays are prevented from the incidence by the electrodes and the like, which makes it impossible to obtain a sufficient sensitivity to extremely weak energy rays.
To solve this problem, a method of applying the energy rays from the back surface side is adopted in some of CMOS image sensors. In this case, the thickness of the semiconductor substrate on the photodiode on the back surface side is reduced to about 20 μm by a chemical etching while its peripheral portion is caused to remain. This enables signal charges generated by the energy rays applied from the back surface side to be read. This method makes it possible to suppress a reduction in detection sensitivity to the energy rays due to the electrodes and the like.
In the surface layer of a photo-detection part in the back side illuminated CMOS image sensor, a p+ type semiconductor layer (hereinafter referred to as a “p+ layer”) needs to be formed as an inversion layer for increasing a photosensitivity to the wavelength of each light and for preventing a signal color mixture between adjacent photodiodes. When the p+ layer is formed, a heat treatment for activating the p+ layer is necessary. However, in a conventional heat treatment method, there is a problem that the entire device is heated during the heat treatment for the activation of the p+ layer, which causes an adverse impact on the peripheral circuit device.
Note that JP-A 2009-111118 (KOKAI) discloses an example of a method of manufacturing a back side illuminated imaging device, the method including steps of forming a first pixel separation region by introducing impurities into a semiconductor substrate, forming a first epitaxial growth layer on a surface of the semiconductor substrate, forming a second pixel separation region so that the second pixel separation region penetrates the first epitaxial growth layer to contact with the first pixel separation region, and forming a photoelectric conversion part and a peripheral circuit part within the semiconductor substrate defined by the first and second pixel separation regions. The first and second pixel separation regions are formed, for example, by an ion implantation process and an activation annealing process.